求助：第 5 课，根据你写的 async 示例，我写了一个小爬虫来针对 cnode，我怎么才能证明它确实是限制在 5 个请求上？

var cheerio = require('cheerio'); var superagent = require('superagent'); var url = require('url'); var async = require('async');

var cnodeUrl = 'https://cnodejs.org/'; var topicUrls = [];

superagent.get(cnodeUrl) .end(function(err,res){ if(err){ return console.error(err); } // var topicUrls = [];
var $ = cheerio.load(res.text); $('#topic_list .topic_title').each(function(idx,element){ var $element = $(element); var href = url.resolve(cnodeUrl,$element.attr('href')); topicUrls.push(href); });

async.mapLimit(topicUrls,5,function(url,callback){ console.time("耗时"); superagent.get(url) .end(function(err,res){ if(err){ return console.error(err); }
console.log(url + "1"); var $ = cheerio.load(res.text); var content = []; // var element; // var $element = $(element); content.push({ title: $('.topic_full_title').text().trim(), href: url, comment: $('.reply_content').eq(0).text().trim(), });

     //  console.log(idx + "1111");

        callback(null,content);
  });
  console.timeEnd("耗时");       

},function(err,result){ console.log(err); console.log(result); });

});